Multiservice switches used, for example, by communications providers in wide area networks typically provide a number of different interfaces for incoming and outgoing communications traffic to the core switching fabric in order to accommodate customer needs. These interfaces can range, for example, from high rate optical trunking ports to lower rate electrical interfaces. In general, the different interfaces are provided through service specific equipment grouped together on what are termed “service shelves”, where the service shelves then couple to the switching core. A typical service shelf will include the physical layer interface which couples to higher layer service cards (e.g. layer 2 or 3 for ATM or IP) and then to the switching core. Failure protection of equipment utilized in multiservice switches usually in the form of redundant circuit paths is also extremely important in order to provide the type of reliability that is necessary for these switches. Accordingly, extra service cards (or protection cards) are often provided within a service shelf to allow for the required protection.
In prior art multiservice switches of the type described above, the service cards from the service shelves are directly connected either logically or physically to a core port on the switching core. In accordance with this type of connection, a service card failure makes the core port(s) having the failed card thereon unavailable to the user which in turn degrades overall system bandwidth. The manner in which prior art systems provide service card redundancy is considered a major limitation in that a significant amount of core bandwidth is wasted upon failure of a service card. In addition, core bandwidth is wasted by the need to dedicate additional core ports in order to provide redundancy. Accordingly, there is a need to preserve maximum overall system bandwidth in a packet switching system while at the same time incorporating protection of various service modules.